1. Field of the Invention
The invention relates to a high-resolution synthetic aperture radar device and an antenna for a high-resolution synthetic aperture radar device.
2. Discussion of Background Information
In synthetic aperture radar (SAR), an object, such as, for example, the earth's surface, is scanned by a short moving antenna, via which pulse signals, i.e., pulses are emitted at a defined time interval and the echo signals, i.e., the pulse signals reflected by scanned objects, are received. The direction of movement of the short antenna is also referred to as azimuth or along track. An image of the scanned object is calculated for each area illuminated and scanned by the antenna by an SAR processor through corresponding data processing of the echo signals. For example, SAR systems are used for measuring and imaging the earth's surface by satellites.
In SAR the important parameters are the azimuth resolution, the swath width of the scan and the geometric resolution in the range. The decisive factor for the geometric resolution is the bandwidth of the emitted pulse signals. The pulse repetition frequency (PRF) determines the scanning rate. With conventional SAR systems, the smallest azimuth resolution (along track) and the largest swath width (across track) that can be achieved at the same time are coupled to one another in that a high PRF is necessary for a high azimuth resolution, but a low PRF is necessary for a large swath width. In other words, with conventional SAR a high azimuth resolution determines a small swath width.
This conflict can be resolved by a so-called high-resolution wide-swath (HRWS) SAR, such as is known, for example, from EP 1 241 487 A1. The HRWS SAR is operated with additional receive (RX) antennas or receive apertures, i.e., several, in particular three, azimuth apertures, which makes it possible to reduce the PRF without reducing the azimuth resolution. Furthermore, the instrument is operated bistatically, i.e., with separate transmitting (TX) and receiving (RX) antennas. The elevation, i.e., the measurement in the transverse direction to the azimuth direction of the TX antenna is reduced in order to illuminate a large swath width, and the elevation of the RX antenna is correspondingly increased in order to maintain the sensitivity of the instrument. Finally, each azimuth aperture is divided into several sub-apertures in order to be able to scan a broad swath by digital beam forming (DBF). However, one disadvantage of the HRWS SAR lies in the large antennas, which in particular with satellite-based SAR lead to heavy and thus expensive payloads.